Permanent lenke

Åpne

Dato

2007-11-29

Type

Journal articleTidsskriftartikkelPeer reviewed

Forfatter

Cannon, P. S.; Hall, Chris; Brekke, Asgeir

Sammendrag

We have examined the long time series of observations
of E-region virtual height (1948–2006) and critical frequency
(1935-2006) hitherto made by the Tromsø ionosonde
at 70 degrees N, 19 degrees E. Combining a simplistic trend analysis with
a rigorous treatment of errors we identify a negative trend
in critical frequency. While a similar analysis of the virtual
height h'E also suggests a negative trend, a closer examination
reveals a possible weak positive trend prior to ~1975
and a strong negative trend from ~1975 to present. These
two metrics of essentially the same feature of the ionosphere
do not exhibit the same signature since critical frequency is
controlled by photochemistry within the E-layer while height
is controlled by pressure level. We further find that the trend
in critical frequency is a daylight/summer phenomenon, no
significant trend being evident in the winter subset of the
data. On the other hand, the trends in virtual height are independent
of season/daylight.

Beskrivelse

This is the publishers version/PDF (published in Annales Geophysicae, an open access journal of the European Geosciences Union)